0709_2_mica

Microsporum canis differs from Microsporum audouinii by perforating hair and growing on polished rice grains. Trichophyton rubrum is a very variable organism and many characteristics either overlap or are inconsistent 5. September 2007
On Sabouraud's dextrose agar, colonies are flat to slightly raised, white to cream, suede-like with a pinkish-red re- 0709-2 Microsporum canis
verse. Microscopically, most cultures have numerous clavate to pyriform microconidia and moderate numbers of HISTORY This sample was sent as scalp scraping culture isolate.
smooth, thin walled multiseptate, slender cylindrical mac- CMPT QA: Pure growth of 4+ Microsporum canis viable for 36 days. roconidia. Older cultures may show numerous chlamy-
dospores with few clavate to pyriform microconidia. In- Reference Laboratory: Growth of Microsporum canis.
vaded hairs show ectothrix or endothrix infection but do Results received and media and methods noted are listed in Table 1. not fluoresce under Wood's ultra-violet light. Urease is
There was one misidentification. In a previous challenge with this fun- positive at 7 days for one variant of T. rubrum.
gus, Mycology Plus 0501-2 Skin Scraping (Torso), all participants
identified the genus correctly and all but one reported M. canis.
CLINICAL SIGNIFICANCE Microsporum canis is a
IDENTIFICATION Microsporum differs from Trichophyton and dermatophyte which causes ringworm of the scalp and
Epidermophyton by having spindle-shaped macroconidia with ech- skin in children and has been occasionally reported as
inulate to rough walls.
the cause of nail infections 1. Tinea or ringworm is the result of the host reaction to the enzymes released by the Colony morphology 1-3 On Sabouraud's dextrose agar, Micro- fungus during the digestive process 2. Rarely, myce-
sporum canis matures within 6 to 10 days producing colonies that toma-like lesions have been observed in immunocom- are flat, spreading, white to cream-coloured, with a dense cottony, promised hosts 3. Microsporum canis is a complex spe- granular to coarsely fluffy to hairy surface which may show some cies with several variants. M. canis var. canis is the radial grooves. Colonies usually have a bright golden yellow to most commonly encountered species in human infec- brownish yellow reverse pigment, but non-pigmented strains may tions and is distributed world wide; however, it is less also occur. There are variants that are slow growing, heaped and common in North America, the United Kingdom, and folded, yellow surface, no reverse pigment, macroconidia absent, Scandinavia than the rest of the world. but which revert to typical colony on rice grains. Most M. canis infections in humans are acquired from Microscopic morphology 2,3 Microsporum canis produces septate infected dogs or cats. In an M. canis outbreak affecting
hyphae, macroconidia, and few or rare microconidia. Macroconidia are 15 people and 2 dogs with rapid transmission, the re- typically long spindle-shaped, with 5-15 cells, verrucose, thick-walled searchers noted that family pets may have acted as inter- and often have a terminal knob . The septal walls are thin. Microconidia mediate hosts, facilitating transmission between human are rare, unicellular and clavate to pyriform in shape. Raquet hyphae, contacts 6. They concluded that while M. canis is an infre- nodular bodies, and chlamydospores may be present. quent cause of tinea infections in the USA, it should re- Macroconidia and/or microconidia are often not produced on pri- main in the differential diagnosis when a fungal infection mary isolation media and it is recommended that sub-cultures be presents in an atypical fashion. From the sanitary point of made onto boiled polished rice grains to stimulate sporulation. view, isolation of either an anthropophilic or zoophilic Tests 1,4,5
species requires different interventions 7. No special growth factor is required to grow Microsporum canis. TREATMENT 7 Griseofulvin has been established as a
• BCP-milk-solids-glucose agar: no change in pH safe and effective drug for children, when prescribed in doses from 20 to 25 mg per kilogram of body weight. • Hair perforation: positive. Invaded hairs show an ectothrix However, due to side effects such as headaches and infection and fluoresce a bright greenish-yellow under Wood's gastrointestinal disturbances, or even idiosyncratic ones, ultra-violet light. • Rice grains: a deep yellow pigment is typically produced 1,5 Table 1. 0709-2 Identification results received and media and methods noted.
Identification
No. of labs
Media & ID Methods
DTM, Litman oxgall medium, Mycosel agar, PDA, 30oC, urea; IMA, 30oC; IMA, 30oC, PDA; IMA 25oC, 37oC; BHI w/ chloramphenicol, cycloheximide, PDA, SAB, 25oC & 37oC; Littman oxgall, Mycosel, 25oC;PDA, Mycobiotic Agar with thiamine & Inositol, 27oC;IMA, Mycosel, 29oC Key: PDA - potato dextrose agar; IMA - ihibitory mould agar; DTM - dermatophyte test medium; BCP - bromcresol purple media FSA – fungal selective agar CMPT Mycology Plus 0709-2 M. canis (continued from page 1) such as hypersensitivity it is not always well tolerated. Under such
circumstances, terbinafine, itraconazole and even fluconazole are
alternatives. Oral therapy with terbinafine and itraconazole are very
widely used for treatment of Microsporum infections; however,
treatment failure with terinafine has been reported for M. canis.
Itraconazole, in the dose of 5 mg per kilogram of body weight is
effective, even though there may be restrictions to its use in virtue
of its cost or less experience of its use in children. Topical therapy
with Tea Tree Oil, might be considered before oral therapy 8.

REFERENCES
1. Summerbell RC, Weitzman I, Padhye AA. 2007. Trichophyton,
Microsporum, Epidermophyton, and Agents of Superficial My-coses. pp. 1874-1897. In PR Murray et al. (eds.) Manual of Clinical Microbiology. 9th ed. ASM Press. Washington, DC. 2. Larone DH. 2002. Medically Important Fungi. 4th ed. ASM 3. http://www.doctorfungus.org/thefungi/microsporum_canis.htm 4. http://www.provlab.ab.ca/mycol/tutorials/derm/7case.htm 5. http://www.mycology.adelaide.edu.au/Fungal_Descriptions/ Dermatophytes/Microsporum/Microsporum_canis.html 6. Chiller K, Resneck J, Chiller T, Aly R. 2002. An outbreak of Microsporum canis in the community demonstrating rapid transmission. Exogenous Dermatology. 1:18-21. 7. Marques SA. 2005. Tinea capitis: epidemiological and ecologi- cal aspects of cases observed from 1983 to 2003 in the Botucatu Medical School. An Bras Dermatol. 80:6. p. 597-602. h t t p : / / 7 2 . 1 4 . 2 5 3 . 1 0 4 / s e a r c h ?q=cache:edS77LHGmB8J:www.scielo.br/pdf/abd/v80n6/en_v80n06a05.pdf+microsporum+canis+canada&hl=en&ct=clnk&cd=40&gl=ca 8. Hammer KA, Carson C, Riley T. 2002. In vitro activity of Me-
laleuca alternifolia (tea tree) oil against dermatophytes and other filamentous fungi. J Antimicrob Chem. 50. p. 195-199. Rice Grain Test To induce sporulation and for differentiation of M. canis and M. audouinii 1,5.
Media Preparation:
1. Place approximately 1/2 teaspoon polished (white) rice grains into wide neck 20 mL vials.
2. Add 8 mL distilled water to each vial. (Note: Adding Tween 80 can enhance chlamydospore formation in Candida
3. Lid, then slope on racks ensuring rice grains are evenly distributed.
4. Autoclave racks at 121oC for 15 minutes.

Rice Grain Test Method
1. With a long-handled inoculating needle, transfer a small portion of the isolate to be tested to a vial containing sterile
2. Incubate the flask at 30oC and examine for growth for 8-10 days.
Results
a. Positive - M. canis—Rapid growth on rice grains, typically produce many conidia and a bright yellow pigment.
b. Negative - M. audouinii—Absence of growth with or without a brown discoloration of the rice grains at the site of
inoculation.
Quality Control - Known isolates of M. canis and M. audouinii are run concurrently with each rice grain test.

Source: http://cmpt.ca/pdf/pdf_mycology/myc2007/0709_2_mica.pdf